Weird TPS Issue and Surging at 65-70mph Cruise
 

Dealing with a strange issue I suspect may be related to sticking throttle cables or perhaps linkage:

- Engine starts, idles and runs fine when cold.

- During operating temperature the car drives fine in stop and go traffic.

- On freeway, car shutters on cruise at 65-70mph. Accelerating harder to 80mph fixes this. The position of the gas pedal (such as feathering the pedal) at lower speed I suspect is triggering an on/off issue with the idle switch while adding more load to the engine keeps it off idle (naturally)

- When disconnecting the LH and EZK harnesses I can verify with an ohmmeter the idle switch is operating correctly.

- In checking the cables, the gas pedal cable had virtually no slack. I suspect this may be the issue as the engine warms up, causing intermittent contact with the idle switch.

I added a small amount of slack with 3/4 of a turn at the firewall. Looks like the pedal travel is ever so slightly longer now to move the linkage. Car seems to run fine warm now but is not as responsive. But what are the chances heat expansion applying tension to the gas pedal cable would trigger an on/off issue with the idle switch and cause massive surging?

Is this something else? And yes I can confirm the car does not have TBF. Intake service was done back in 2010, and only had 4,000 miles on it since. All new vacuum lines, idle stabilizer valve and throttle switch.

Any chance it's the TPS itself? Is the part original to the car, or has it been replaced recently?

Good luck

I replaced it in 2010 when I did the intake service. Come to think of it, I don't think there was one part I didn't replace under that hood related to the LH and EZK injection.

MAF age?

And does an ECU reset clear the stuttering?

MAF is the same age and mileage (2010 and 4k miles old). Disconnecting the battery to reset the O2 loop doesn't affect it (new O2 sensor also).

Im chasing down two issues. ONE is a stuttering.

ECU reset fixes it, it's a Porken chip code issue.

I have Ken's S300 EZK chip in. I haven't put the LH one in since I confirmed 2 of my 24 lbs. Injectors refurbished don't click. Need to replace them before installing. Until then, diagnostics and repair are priority.

Is your car doing the same thing at a certain speed? Next time you're out in Marin PM, me. Witnesses are needed lol

I will ring ya! My Pken chip is the adaptive timing one. A few hundred miles and it will develop a studder mid throttle, and slowly get worse all OVER the place. Reset ECU, gone..
I just did a 5600 mile road trip for a month in all sorts of weather, if ambient was over 70d, it was more prevalent then if under 70 degrees...BUT on Aaron Bunch's dyno in Denton, we did a full reset to peak adaptation # of runs ont he dyno, and Ken's **** works...I out pulled a lot of "tuned" 928s in his dyno library with ease.

I should tag him in Pkens chip thread...

Im in Socal until Monday, and the car is in the shop (Deer hit in Feb, finally getting repaired)...

Im sure it will be done, and I will guaranteed be up there in the 928 at the next race event:

1. May 21-22 Sonoma
   
   

Wow, just how much did you gain with the new ezk chip? I have my S300 and factory cats back on, with my x-pipe merged to my single 3" after cats the car was spinning tires after 4k rpm.

I'm hoping you got the same result with the upgrade regardless of the mid power issue.

Id have to find a windows machine to load the dyno viewer software on..but 87 Auto, 281Hp and unknown Tq...and Ive spent a ton of runs on fuel...and A/F had no room for improvement..it was dialed in.

That's about 331HP at the flywheel at 18% drivetrain factor! :eek:

Do you have an x-pipe too?

I do, and cats, and the large quiet resonators...and OE muffler.